Method of reducing friction losses in flowing liquids

ABSTRACT

A method of reducing friction losses in aqueous and nonaqueous liquids is disclosed. A certain polymeric material has heretofore been admixed to this end with flowing liquids, such polymer being dissolvable to form a solution. The prior art method is effective for friction loss reduction, but has a drawback in that the polymer is susceptible to scission of its chains under shear stress and hence is unstable in the solution. The invention disclosed is based on the discovery that friction losses in liquids can be reduced with maximum stability by adding to a liquid a predetermined amount of selected organo-polymeric microfibrils which are insoluble but highly dispersible in the liquid. The method of the invention may be applied for instance in the transport of various liquids and crude oils through pipelines and also in the circulation of aqueous and nonaqueous lubricants.

FIELD OF THE INVENTION

This invention relates to a method of reducing friction losses inflowing liquids.

PRIOR ART

It is known that friction loss in flowing liquids can be reduced byintermixing therewith small amounts of a certain soluble polymericmaterial. In such instance, the polymeric material dissolves in theliquid and forms a solution. When the solution is conducted through apipeline or other restricted space, the dissolved polymers serve toeliminate or alleviate the tendency of the flow of the solution tobecome turbulent; that is, to maintain the flow laminar so as tominimize friction loss. This is the phenomenon called the TOMS effectafter the discoverer.

The prior art method, however, is not quite satisfactory in that thepolymer is susceptible to scission of its chains due to shear stressapplied during flow of the solution, leading to instability in thesolution. This problem has yet to be solved despite many attempts thathave been made with different kinds of polymers.

The present invention seeks to provide a method of reducing frictionlosses in flowing liquids which is free of the foregoing problem andwhich can exhibit excellent stability in a given liquid.

SUMMARY OF THE INVENTION

According to the invention, there is provided a method of reducingfriction losses in flowing liquids, characterized by adding to a liquidan organo-polymeric microfibril material in an amount of 0.1 ppm-5percent by weight of said liquid, said material being insoluble andhighly dispersible in said liquid.

BEST MODE OF EMBODYING THE INVENTION

The term liquid as used herein includes aqueous or nonaqueous liquidssuch as oils, lubricants, aqueous lubricants, crude oil, petroleumfractions, solvents and the like.

The term organo-polymeric microfibril as used herein designates a solidorganic polymer in the form of microfibrils having an average diameterin the range of 10 Å-5 μm, preferably 50 Å-1 μm, more preferably 100Å-1,000 Å, an average length in the range of 1,000 Å-3 mm, preferably 1μm-500 μm, and an aspect ratio (length/diameter) of 10-1,000,000.

Polymeric microfibrils of diameters smaller than 10 Å are difficult tomake and if not, would be susceptible to scission under shear stresswhen added to a liquid. Greater diameters than 5 μm would inviteprecipitation of the microfibrils in the liquid.

Polymeric microfibrils of lengths less than 1,000 Å would fail tosuppress turbulence in the flowing liquid. Greater lengths than 3 mmwould result in coagulated, precipitated microfibrils in the liquid.

Polymeric microfibrils of aspect ratios smaller than 10 would beineffective for turbulence reduction. Excessive aspect ratios would leadto entanglement of individual microfibrils and hence precipitation inthe flowing liquid.

Polymeric materials to be processed into microfibrils according to theinvention should be insoluble but highly dispersible in a given liquid.There may be used for example polyethylene, polypropylene, polystyrene,polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene,polyethylene terephthalate, polymethylmethacrylate, nylon, polycarbonateand copolymers or blends thereof.

Polymeric compounds known for their heat resistance may also be usedwhich include aromatic polyamides, aromatic polyethers,polyetheretherketones, aromatic polyesters, aromatic polyimides andpolybenzoimidazoles.

Other polymeric materials that have been found particularly preferableare those which are capable of forming a liquid crystal. Specificexamples include aramide fibers such as poly-p-phenylene terephthalamidewet spun from sulfuric acid liquid crystal solution andpolybenzobisthiazole wet spun from polyphosphoric acid liquid crystalsolution.

Microfibrils formed from polymeric solutions or melts in a liquidcrystal state have high molecular orientation and hence high strength sothat when placed in a liquid, they can resist scission against increasedshearing force applied during flow of the liquid.

By "highly dispersible" is meant the state of polymeric microfibrilswhich can be determined by an experiment in which 100 ppm of a polymericmicrofibril material is added to the liquid and stirred vigorously forfive hours, and thereafter 200 ml of the resulting suspension is takeninto a tapped, graduated cylinder of Grade No. 200 (inside diameter 37mm, capacity 200 ml) and held still for one hour. If the amount of thepolymeric material that has precipitated is less than 50 ppm, then thisis taken to mean that the material is highly dispersible. A choice ofpolymeric microfibril materials depends upon a particular kind of liquidin which they are used.

What is meant by the microfibrils being "insoluble" in a liquid may bedetermined by an experiment in which 5 weight percent of a polymericmicrofibril material is added to the liquid and stirred vigorously forfive hours at a working temperature, followed by filtration and drying,whereupon the material is measured for weight reduction. If thisreduction is less than 10 weight percent of the original weight, thenthe microfibril material is regarded as insoluble.

There is no restriction imposed upon how to make the polymericmicrofibril material. It may be spun by jet stream from polymeric melts,or formed by mechanical grinding of polymeric fibers, or prepared bydropwise addition of a polymeric solution to a coagulated liquid underhigh speed agitation or supersonic radiation. These methods may becombined at will.

The above described methods are also applicable to polymeric solutionsor melts in a liquid crystal state. Fibers obtained by liquid crystalspinning may be cut and ground, in which instance the fibers may beground while being swollen.

In order to improve dispersibility of the microfibril material in aliquid and also to enhance stability of the resultant suspension, thematerial may be treated with a suitable surfactant, or chemicallymodified, or physically treated as by corona discharge.

The rate of the polymeric microfibril material to be added is in therange of 0.1 ppm-5 percent, preferably 1 ppm-1 percent.

Smaller amounts would fail to inhibit turbulent flow, and larger amountswould lead to coagulation and hence precipitation.

The method of the invention finds effective application where the liquidis transported through a pipeline, particularly when its Reynolds numberexceeds 1,000. The Reynolds number is one which can be determined from aradius of a pipe with respect to a kinematic viscosity and a velocity ofa liquid to be flowed through the pipe, a diameter of the pipe and thelike. In the case of lubrication of bearings in large, high-speedindustrial machinery, the lubricant has a Reynolds number usually inexcess of 1,000 or even 2,000 beyond the critical limit of a laminarflow; therefore, increased power would be required to compensate forfriction losses, or sometimes the bearings would get overheated,affecting the stability or service life of the equipment. The inventionis directed to elimination or alleviation of such adverse situations.

The invention will be further described by way of the followingexamples.

COMPARISON EXAMPLE 1

A homogeneous solution was prepared by dissolving polyisoprene incyclohexane under conditions shown in Table 1. The solution wascirculated by a metering pump through a circular loop of pipe of thedimensions indicated in Table 1 at the rate of flow and temperaturetabulated. Pressure drop across the loop was measured by pressure gageseach at the inlet and outlet of the pump. The rate of reduction offriction loss in the circulating solution may be determined by theequation: ##EQU1## where ΔP is a pressure drop with an additive(polyisoprene in the case of Comparison Example 1) and ΔPo is a pressuredrop without such additive. Rate A is a parameter representing the TOMSeffect that turbulent flow is suppressed. Rate A in Comparison Example 1was quite satisfactory in the first cycle of circulation of the liquid,but sharply declined with 1,000 cycles of circulation due to scission ofpolyisoprene molecules under the influence of shear stress.

INVENTION EXAMPLE 1

A stable suspension was prepared by adding polypropylene microfibrils tocyclohexane as shown in Table 1 and tested in a manner similar toComparison Example 1. Rate A was by far more satisfactory than that inComparison Example 1 especially after 1,000 cycles of circulation of theliquid. This is believed to be due to polypropylene being in the form ofmicrofibrils which are highly resistant to shear stresses, as contrastedto polyisoprene being of a molecular order.

INVENTION EXAMPLE 2

A stable suspension was prepared, as shown in Table 1, by blendingcyclohexane with polymeric microfibrils of aramide (DuPont's "Kevlar49", liquid crystal spun polymer, poly-p-phenylene terephthalamide). Thesuspension was subjected to the same test as in Comparison Example 1.Rate A was quite satisfactory with the same levels of reductionexhibited in the first cycle and after 1,000 cycles of circulation, andyet was excellent as compared to that in Invention Example 1. This isbelieved to accrue from high strength of this polymeric microfibrilmaterial.

INVENTION EXAMPLES 3-5

As shown in Table 2, Murban crude oil was added with aramidemicrofibrils (DuPont's "Kevlar" 49") to make stable suspensions. Therespective suspensions were tested using the temperature, flow rate andpipe tabulated. Rate A was quite satisfactory in each instance withoutdeclining even after 1,000 cycles of circulation.

INVENTION EXAMPLES 6-9

To turbine oil was added microfibrils of "Kevlar" aramide, high densitypolyethylene, polyethylene terephthalate and nylon-6, respectively, asshown in Table 3. The respective suspensions were tested for frictionloss reduction with results tabulated.

Rate A was quite satisfactory in each instance. Particularly excellentwere the suspensions in which "Kevlar" microfibrils were used. Rate Ashowed no appreciable decline even after 1,000 cycles of circulation.

INDUSTRIAL APPLICABILITY

The method of the invention can reduce friction losses in the transportor circulation of various liquids. It may be applied for instance in thetransport of crude oils from oil-wells through pipelines to tankers ortankers to storage tanks, thereby saving energy required to transportthe crude oils and further providing increased flow rates. It may alsobe applied to the circulation of lubricating oils such as turbine oils,gear oils, compressor oils and bearing oils whereby high-load,high-speed operation can be stably maintained for prolonged periods oftime.

                                      TABLE 1                                     __________________________________________________________________________                                                Friction loss                                                 Inside          reduction rate (%)                                            diameter        After 1st                                                                           After 1,000                                             and length                                                                          Temp.                                                                             Flow rate                                                                           cycle of                                                                            cycles of                   Example                                                                              Base liquid                                                                          Additive      of pipe                                                                             (°C.)                                                                      (l/min.)                                                                            circulation                                                                         circulation                 __________________________________________________________________________    Comparison                                                                           Cyclohexane                                                                          Polyisoprene (average MW:                                                                   φ3.63 mm                                                                        25  50    11    2.5                         Example 1     400,000)      1.2 m                                                           400 ppm added                                                                 Dissolved and homogeneous                                                     solution formed                                                 Invention                                                                            Cyclohexane                                                                          Polypropylene microfibrils                                                                  φ3.63 mm                                                                        25  50    13    6.5                         Example 1     (diameter: 200Å,                                                                        1.2 m                                                           length: 12 μm)                                                             400 ppm added                                                                 Not dissolved and stable                                                      suspension formed                                               Invention                                                                            Cyclohexane                                                                          "Kevlar" microfibrils                                                                       φ3.63 mm                                                                        25  50    16    16                          Example 2     (diameter: 150Å,                                                                        1.2 m                                                           length: 2 μm)                                                              400 ppm added                                                                 Not dissolved and stable                                                      suspension formed                                               __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________                                              Friction loss                                                 Inside          reduction rate (%)                                            diameter        After 1st                                                                           After 1,000                                             and length                                                                          Temp.                                                                             Flow rate                                                                           cycle of                                                                            cycles of                     Example                                                                             Base liquid                                                                           Additive    of pipe                                                                             (°C.)                                                                      (l/min.)                                                                            circulation                                                                         circulation                   __________________________________________________________________________    Invention                                                                           Murban crude                                                                          "Kevlar" microfibrils                                                                     φ15.6 cm                                                                        25  2,980 25    25                            Example 3                                                                           oil     (diameter: 900Å,                                                                      1.2 m                                                             length: 450 μm)                                                            0.5 ppm added                                                                 Not dissolved and stable                                                      suspension formed                                               Invention                                                                           Murban crude                                                                          "Kevlar" microfibrils                                                                     φ15.6 cm                                                                        25  2,980 67    66                            Example 4                                                                           oil     (diameter: 10Å,                                                                       5 m                                                               length: 1,200Å)                                                           5 wt. % added                                                                 Not dissolved and stable                                                      suspension formed                                               Invention                                                                           Murban crude                                                                          "Kevlar" microfibrils                                                                     φ15.6 cm                                                                        25  2,980 56    56                            Example 5                                                                           oil     (diameter: 5 μm,                                                                       5 m                                                               length: 3 mm)                                                                 1 wt. % added                                                                 Not dissolved and stable                                                      suspension formed                                               __________________________________________________________________________

                                      TABLE 3                                     __________________________________________________________________________                                              Friction loss                                                 Inside          reduction rate (%)                                            diameter        After 1st                                                                           After 1,000                                             and length                                                                          Temp.                                                                             Flow rate                                                                           cycle of                                                                            cycles of                     Example                                                                             Base liquid                                                                          Additive     of pipe                                                                             (°C.)                                                                      (l/min.)                                                                            circulation                                                                         circulation                   __________________________________________________________________________    Invention                                                                           Turbine oil*                                                                         "Kevlar" microfibrils                                                                      φ12.7 mm                                                                        40  112   75    75                            Example 6    (diameter: 500Å,                                                                       3 m                                                              length: 200μm)                                                             100 ppm added                                                                 Not dissolved and stable                                                      suspension formed                                                Invention                                                                           Turbine oil*                                                                         High density polyethylene                                                                  φ12.7 mm                                                                        40  112   36    17                            Example 7    microfibrils (diameter:                                                                    3 m                                                              200Å, length: 20 μm)                                                   10 ppm added                                                                  Not dissolved and stable                                                      suspension formed                                                Invention                                                                           Turbine oil*                                                                         Polyethylene terephthalate                                                                 φ12.7 mm                                                                        40  112   22    11                            Example 8    microfibrils (diameter:                                                                    5 m                                                              300Å, length: 3,000Å                                                  5 ppm added                                                                   Not dissolved and stable                                                      suspension formed                                                Invention                                                                           Turbine oil*                                                                         Nylon-6 microfibrils                                                                       φ12.7 mm                                                                        40  112   31    15                            Example 9    (diameter: 100Å,                                                                       3 m                                                              length: 1 μm)                                                              50 ppm added                                                                  Not dissolved and stable                                                      suspension formed                                                __________________________________________________________________________     *FBK Turbine 32 made by Nippon Oil Co., Ltd.                             

I claim:
 1. A method of reducing friction losses in a flowing liquid,which consists essentially of adding to said liquid an organo-polymericmicrofibril material of average diameter 10 Å-5 micrometers, an averagelength of 1,000 Å-3 mm and an aspect ratio of 10-1,000,000 in an amountof 0.1 ppm-5 percent by weight of said liquid, said material beinginsoluble and highly dispersible in said liquid and wherein saidpolymeric material is poly-p-phenylene terephthalamide wet spun fromsulfuric acid liquid crystal solution of polybenzobisthiazole wet spunfrom polyphosphoric acid liquid crystal solution.